The tumor-necrosis factor (TNF)-related cytokines are mediators of host defense and immune regulation. Members of this family exist in membrane-anchored forms, acting locally through cell-to-cell contact, or as secreted proteins capable of diffusing to more distant targets. A parallel family of receptors signals the presence of these molecules leading to the initiation of cell death or cellular proliferation and differentiation in the target tissue. Presently, the TNF family of ligands and receptors has at least 11 recognized receptor-ligand pairs, including: TNF:TNF-R; LT-a:TNF-R; LT-α/β:LT-β-R; FasL:Fas; CD40L:CD40; CD30L:CD30; CD27L:CD27; OX40L:OX40 and 4-1BBL:4-1BB.
TNF family members can best be described as master switches in the immune system controlling both cell survival and differentiation. Only TNF and LT-a are currently recognized as secreted cytokines contrasting with the other predominantly membrane-anchored members of the TNF family. While a membrane form of TNF has been well characterized and is likely to have unique biological roles, secreted TNF functions as a general alarm signaling to cells more distant from the site of the triggering event. Thus TNF secretion can amplify an event leading to the well-described changes in the vasculature lining and the inflammatory state of cells. In contrast, the membrane bound members of the family send signals though the TNF type receptors only to cells in direct contact. For example T cells provide CD40 mediated “help” only to those B cells brought into direct contact via cognate TCR interactions. Similar cell-cell contact limitations on the ability to induce cell death apply to the well-studied Fas system.
Most membrane-associated LT-α/β complexes (“surface LT”) have a LT-α1/β2 stoichiometry. (Browning et al., Cell, 72, pp. 847-56 (1993); Browning et al., J. Immunol., 154, pp. 33-46 (1995)). Surface LT ligands do not bind TNF-R with high affinity and do not activate TNF-R signaling. The LT-β receptor (LT-β-R), does however bind these surface lymphotoxin complexes with high affinity (Crowe et al., Science, 264, pp. 707-10 (1994)).
LTβ-R signaling, like TNF-R signaling, has anti-proliferative effects and can be cytotoxic to tumor cells. In applicants' co-pending U.S. application Ser. No. 08/378,968, compositions and methods for selectively stimulating LT-β-R using LT-β-R activating agents are disclosed. LT-β-R activating agents are useful for inhibiting tumor cell growth without co-activating TNF-R-induced proinflammatory or immunoregulatory pathways.
Recent gene targeting studies suggest a role for LT-α/β in the development of secondary lymphoid organs. (Banks et al., J. Immunol., 155, pp. 1685-1693 (1995); De Togni et al., Science, 264, pp. 703-706 (1994)). Indeed, LT-α-deficient mice lack lymph nodes (LN) and Peyer's patches (PP). Moreover, their spleens have disrupted architecture and the expression of functional markers on cells of the splenic marginal zone is altered. (Banks et al., 1995; De Togni et al., Science, 264, pp. 703-706 (1994), Matsumoto at al., Science, 271, pp. 1289-1291 (1996)). None of these characteristics have been described for either of the TNF receptor knock out mice. (Erickson et al., Nature, 372, pp. 560-563 (1994); Pfeffer et al., Cell, 73, pp. 457-467 (1993); Rothe et al., Nature, 364, pp. 798-802 (1993). Applicants have recently defined a role for membrane LT-α/β complexes in secondary lymphoid organ development by showing that the progeny of mice which had been injected during gestation with a soluble form of mouse LT-β-R fused to the human IgG1 Fc portion (LT-β-R-Ig) lacked most lymph nodes and showed disrupted splenic architecture. (Rennert et al, 1996, “Surface Lymphotoxin alpha/beta complex is required for the development of peripheral lymphoid organs.” J. Exp Med, 184: 1999-2006). In another study, mice transgenic for a similar LT-β-R-Ig construct which starts to be expressed three days after birth, were shown to have LN. However, their splenic architecture was disrupted and several markers of splenic marginal zone cells were not expressed (Ettinger et al., “Disrupted splenic architecture, but normal lymph node development in mice expressing a soluble LTβ-R/IgG1 fusion protein”, Proc. Natl. Acad. Sci. U.S.A. 93: 13102-7). Together these data indicate there is a temporal requirement for membrane LT functions to mediate effects on the development of secondary lymphoid organs, but not for effects on splenic architecture.
The TNF system may also function in development of the spleen. Splenic marginal zone cells of TNF-deficient mice do not express macrophage markers or MAdCAM-1 (Alexopoulou et al., 60th Int. TNF Congress, Eur. Cytokine Network, pp. 228 (1996); Pasparakis et al., 60th Int. TNF Congress, Eur. Cytokine Network, pp. 239 (1996)). TNF-R55-deficient mice also lack MAdCAM-1 (but not MOMA-1) staining in the splenic marginal zone. (Neumann et al., J. Exp. Med., 184, pp. 259-264 (1996), Matsumoto et al., Science, 271, pp. 1289-1291 (1996)). The expression of these markers as seen in the spleen of TNF-R75-deficient mice appears normal. (Matsumoto et al., Science, 271, pp. 1289-1291 (1996)).
Lymphoid-like tissues do not only arise as a part of developmental processes but also appear under some pathological circumstances such as chronic inflammation, a process recently termed neolymphoorganogenesis. (Picker and Butcher, Annu. Rev. Immunol., 10, pp. 561-591 (1992), Kratz, et al., J. Exp. Med., 183, pp. 1461-1471 (1996)). TNF family members apparently influence such processes. Mice transgenic for the LT-α gene driven by the rat insulin promoter (RIP-LT) developed LT-induced chronic inflammatory lesions with characteristics of organized lymphoid tissues. (Kratz, et al., J. Exp. Med., 1183, pp. 1461-1471 (1996); Picarella et al., Proc. Natl. Acad. Sci., 89, pp, 10036-10040 (1992)).
The evaluation of LT function during a T cell-dependent immune response, using LT-α-deficient mice, showed the necessity of LT for GC formation, possibly for maintaining an organized follicular dendritic cell (FDCs) structure, and for humoral responses. (Banks et al., J. Immunol., 155, pp. 1685-1693 (1995); Matsumoto et al., Science, 271, pp. 1289-1291 (1996); Matsumoto et al., Nature, 382, pp. 462-466 (1996)). TNF-R55-deficient mice also lack FDCs, fail to develop GC and fail to develop an optimal antibody response to sheep red blood cells (SRBC). This suggests that TNF-R55 might be triggered by soluble LT or TNF signals for most of these responses (Le Hir et al., J. Exp. Med., 183, pp. 2367-2372 (1996), Alexopoulou et al., 60th Int. TNF Congress, Eur. Cytokine Network, pp. 228 (1996); Pasparakis et al., 60th Int. TNF Congress, Eur. Cytokine Network, pp. 239 (1996)).
The LT-β-receptor, a member of the TNF family of receptors, specifically binds to surface LT ligands. LT-β-R binds LT heteromeric complexes (predominantly LT-α1/β2 and LT-α2/β1) but does not bind TNF or LT-α (Crowe et al., Science, 264, pp. 707-10 (1994)). LT-β-R mRNAs are found in the human spleen, thymus and in general organs with immune system involvement. Although studies on LT-β-R expression are in their early stages, LT-β-R expression patterns appear to be similar to those reported for TNF-R55 except that LT-β-R is lacking on peripheral blood T and B cells and T and B cell lines.
Cell surface lymphotoxin (LT) complexes have been characterized in CD4+ T cell hybridoma cells (II-23.D7) which express high levels of LT. (Browning et al., J. Immunol., 147, pp. 1230-37 (1991); Androlewicz et al., J. Biol. Chem., 267, pp. 2542-47 (1992), both of which are herein incorporated by reference). The expression and biological roles of LTβ-R, LT subunits and surface LT complexes have been reviewed by C. F. Ware et al. “The ligands and receptors of the lymphotoxin system”, in Pathways for Cytolysis, Current Topics Microbiol. Immunol., Springer-Verlag, pp. 175-218 (1995) specifically incorporated by reference herein.
LT-α expression is induced and LT-α secreted primarily by activated T and B lymphocytes and natural killer (NK) cells. Among the T helper cells, LT-α appears to be produced by Th1 but not Th2 cells. LT-α has also been detected in melanocytes. Microglia and T cells in lesions of multiple sclerosis patients can also be stained with anti-LT-α antisera (Selmaj et al., J. Clin. Invest., 87, pp. 949-954 (1991)).
Lymphotoxin β (also called p33) is expressed on the surface of human and mouse T lymphocytes, T cell lines, B cell lines and lymphokine-activated killer (LAK) cells. LTβ is the subject of applicants' co-pending international applications PCT/US91/04588, published Jan. 9, 1992 as WO 92/00329; and PCT/US93/11669, published Jun. 23, 1994 as WO 94/13808, which are herein incorporated by reference.
Surface LT complexes are primarily expressed by activated T (helper, Th1, and killer cells) and B lymphocytes and natural killer (NK) cells as defined by FACS analysis or immunohistology using anti-LT antibodies or soluble LT-β-R-Ig fusion proteins. In applicants copending U.S. application Ser. No. 08/505,606, filed Jul. 21, 1995, compositions and methods for using soluble LT-β receptors and anti-LT-β receptor and ligand specific antibodies as therapeutics for the treatment of immunological diseases mediated by Th1 cells are disclosed. Surface LT has also been described on human cytotoxic T lymphocyte (CTL) clones, activated peripheral mononuclear lymphocytes (PML), IL-2-activated peripheral blood lymphocytes (LAK cells), pokeweed mitogen-activated or anti-CD40-activated peripheral B lymphocytes (PBL) and various lymphoid tumors of T and B cell lineage. Engagement of alloantigen-bearing target cells specifically induces surface LT expression by CD8+ and CD4+ CTL clones.
Applicants have described herein several immunological functions for surface LT, and show the effects of LT-α/β binding reagents on the generation and character of immunoglobulin responses, maintenance of the cellular organization of secondary lymphoid tissues including effects on the differentiation state of follicular dendritic cells and germinal center formation, and addressin expression levels which influence cell trafficking. Thus applicants define therapeutic applications for surface LT-α/β and LT-α receptor binding agents.
Studies have shown that B cells are activated in the lymph nodes (LN) and spleen following encounters with various antigens. In a specialized structure called a germinal center which forms in the B cell rich regions of LN and spleen, the B cells mature and memory B cells form (Tsiagbe, et al. Crit. Rev. Immunol. 16, 381-421 (1996)). B cells are capable of undergoing transformation into tumors at most points during their development (Freedman, et al, Cancer Medicine 3rd Ed., pp. 2028-2068 (1994)). Transformation of B cells leads to lymphomas and those derived from B cells in germinal centers are often called follicular lymphomas. The exact delineation of the various subsets of lymphomas is still in transition as more surface markers are found permitting a more precise designation of the cell of origin. Follicular lymphomas can be divided into a number of subgroups based on the stage or type of B cell that is proliferating and the prognosis varies depending on the cell type. Conventional chemotherapy regimes are capable of affecting a cure in many of the patients with low-grade type cells. Nonetheless a portion of these patients are resistant to chemotherapy and have a poor prognosis.
Therefore, despite the progress in treating tumors, there remains a need for a treatment for those tumors especially for those follicular lymphomas typically resistant to chemotherapy, as well as for treatment regimes with fewer side effects than existing therapies.